NeuronLogistic.h

/**
 * DESCRIPTION OF THE CLASS
 *
 * @author Martin Beseda
 * @author Martin Mrovec
 * @author Michal Kravčenko
 * @date 2017 - 2018
 */

#ifndef INC_4NEURO_NEURONLOGISTIC_H
#define INC_4NEURO_NEURONLOGISTIC_H

#include <cmath>

#include "../settings.h"
#include "Neuron.h"

namespace lib4neuro {
    class NeuronLogistic : public NeuronDifferentiable {

    public:

        /**
         * Struct used to access private properties from
         * the serialization function
         */
        struct access;

        /**
         * Constructs the object of the Logistic neuron with activation function
         * f(x) = (1 + e^(-x + b))^(-1)
         */
        LIB4NEURO_API explicit NeuronLogistic();

        /**
         * Evaluates '(1 + e^(-x + b))^(-1)' and stores the result into the 'state' property
         */
        LIB4NEURO_API virtual double activate(double x, double b) override;

        /**
         * Calculates the partial derivative of the activation function
         * f(x) = (1 + e^(-x + b))^(-1)
         * @return Partial derivative of the activation function according to the
         * bias, returns: -e^(b - x)/(e^(b - x) + 1)^2
         */
        LIB4NEURO_API virtual double activation_function_eval_derivative_bias(double x, double b) override;
        /**
         * Calculates d/dx of (1 + e^(-x + b))^(-1)
         * @return e^(b - x)/(e^(b - x) + 1)^2
         */
        LIB4NEURO_API virtual double activation_function_eval_derivative(double x, double b) override;

        /**
         * Returns a pointer to a Neuron with derivative as its activation function
         * @return
         */
        LIB4NEURO_API virtual NeuronLogistic *get_derivative() override;
    };


    class NeuronLogistic_d1 : public NeuronLogistic {

    public:

        /**
         * Struct used to access private properties from
         * the serialization function
         */
        struct access;

        /**
         * Constructs the object of the Logistic neuron with activation function
         * f(x) = e^(b - x)/(e^(b - x) + 1)^2
         * @param[in] b Bias
         */
        LIB4NEURO_API explicit NeuronLogistic_d1();

        /**
         * Evaluates 'e^(b - x)/(e^(b - x) + 1)^2' and returns the result
         */
        LIB4NEURO_API virtual double activate(double x, double b) override;

        /**
         * Calculates the partial derivative of the activation function
         * f(x) = e^(b - x)/(e^(b - x) + 1)^2
         * @return Partial derivative of the activation function according to the
         * bias, returns: (e^(b + x) (e^x - e^b))/(e^b + e^x)^3
         */
        LIB4NEURO_API virtual double activation_function_eval_derivative_bias(double x, double b) override;

        /**
         * Calculates d/dx of  e^(b - x)*(1 + e^(b - x))^(-2)
         * @return  (e^(b + x) (e^b - e^x))/(e^b + e^x)^3
         */
        LIB4NEURO_API virtual double activation_function_eval_derivative(double x, double b) override;

        /**
         * Returns a pointer to a Neuron with derivative as its activation function
         * @return
         */
        LIB4NEURO_API virtual NeuronLogistic *get_derivative() override;
    };


    class NeuronLogistic_d2 : public NeuronLogistic_d1 {

    public:

        /**
         * Struct used to access private properties from
         * the serialization function
         */
        struct access;

        /**
         * Constructs the object of the Logistic neuron with activation function
         * f(x) = (e^(b + x) (e^b - e^x))/(e^b + e^x)^3
         */
        LIB4NEURO_API explicit NeuronLogistic_d2();

        /**
         * Evaluates '(e^(b + x) (e^b - e^x))/(e^b + e^x)^3' and returns the result
         */
        LIB4NEURO_API virtual double activate(double x, double b) override;

        /**
         * Calculates the partial derivative of the activation function
         * f(x) = (e^(b + x) (e^b - e^x))/(e^b + e^x)^3
         * @return Partial derivative of the activation function according to the
         * bias, returns: -(e^(b + x) (-4 e^(b + x) + e^(2 b) + e^(2 x)))/(e^b + e^x)^4
         */
        LIB4NEURO_API virtual double activation_function_eval_derivative_bias(double x, double b) override;

        /**
         * Calculates d/dx of  (e^(b + x) (e^b - e^x))/(e^b + e^x)^3
         * @return (e^(b + x) (-4 e^(b + x) + e^(2 b) + e^(2 x)))/(e^b + e^x)^4
         */
        LIB4NEURO_API virtual double activation_function_eval_derivative(double x, double b) override;

        /**
         *
         * @return
         */
        LIB4NEURO_API virtual NeuronLogistic *get_derivative() override;

    };

}

#endif //INC_4NEURO_NEURONLOGISTIC_H